1. Field
The present disclosure relates to a control apparatus for a continuously variable transmission.
2. Description of the Related Art
As a conventional control apparatus for a continuously variable transmission, for example, the control apparatus described in Japanese Patent No. 4376034 is known. The control apparatus allows the transmission mode of the continuously variable transmission to be switched between a continuous transmission mode and a stepped transmission mode, and controls the transmission ratio of the continuously variable transmission according to the transmission mode currently executed. For example, during execution of the continuous transmission mode, a target rotation speed NCMD is set continuously according to a vehicle speed VP and an accelerator opening AP, and the transmission ratio is controlled so that the engine rotation speed NE follows the target rotation speed NCND.
During execution of the stepped transmission mode, an upper limit rotation speed NLMT and an up shift rotation speed NUP are each determined according to the vehicle speed VP and the accelerator opening AP. In a time period after the engine rotation speed NE reaches the upper limit rotation speed NLMT until the engine rotation speed NE becomes lower than or equal to the up shift rotation speed NUP, transfer torque reduction control process for a start clutch and reduction control process for the engine torque are performed. When the engine rotation speed NE becomes lower than or equal to the up shift rotation speed NUP, the transfer torque reduction control process for the start clutch and the reduction control process for the engine torque are terminated.
The switching control of the transmission mode is performed in the following manner. For example, during execution of the continuous transmission mode, a start rotation speed NSS in the stepped transmission mode is determined according to the vehicle speed VP, and when each of the engine rotation speed NE and the target rotation speed NCMD is higher than the start rotation speed NSS in the stepped transmission mode, and a change amount DTH of a throttle valve opening TH is greater than a predetermined amount DTHSS, the transmission mode is switched from the continuous transmission mode to the stepped transmission mode.
On the other hand, during execution of the stepped transmission mode, when the engine rotation speed NE is lower than or equal to the upper limit rotation speed NLMT, and the change amount DTH of the throttle valve opening TH becomes less than the predetermined amount DTHSS, or when in up shift process, the engine rotation speed NE becomes lower than an end rotation speed NES which is determined according to the vehicle speed VP, the transmission mode is switched from the stepped transmission mode to the continuous transmission mode.